On Mar 26, 5:20*pm, Jim Stewart wrote:
Robin wrote:
I'm working on a little project (a spotlight) that is basically a bit
of aluminium tubing, 50mm ID, 5mm wall thickness. I was wondering the
best way to close the end of the tube that doesn't have the light
shining out. I'm hoping to make it water resistant
...

Turn a plug .002" over and press it in.

Ditto.

If you are unsure of the proper interference fit you could turn the
plug 0.1mm oversize and then cut a crude thread on it to allow it to
squeeze down into the tube more easily. The thread is less
hypersensitive than a smooth cylinder to removing small amounts for
adjustment, because you effectively trim the groove width rather than
the diameter. Since it makes the plug more compliant than the tube the
OD is less likely to bulge.

You're Robin in England, right? I am also conversing with a Robin in
France about ion thrusters for spacecraft.

jsw